The present invention relates to measuring the content of hydrocarbons in gases, and more particularly the present invention relates to measuring the methane-free portion in the hydrocarbon content in gases, such as exhaust fumes, using at least one flame ionization detector.
Flame ionization detectors, in the following simply referred to as FID's, are used for quite a long time as instruments for measuring the hydrocarbon content in gases. These known instruments operate per se without discriminating as far as methane is concerned. Exhaust and emission measurements which are being undertaken at the present time and to an increasing degree for purposes of improving ecology and the environment, have shown that the inherently included methane content influences the measurement to such an extent that measuring the total content in hydrocarbon is really of very little informative value because the methane content is usually comparatively large but methane is not a gas or component which contributes to the contamination of the environment. Also, whenever measurements of exhaust emission of a combustion engine are undertaken, it was found that the exhaust gases contain a significant quantity in methane. Moreover that methane content varies greatly as it depends on the type of engine, on the fuel used, on the operation of conditions generally and also on the equipment destined to remove contaminants. It was found, for example, that the methane content in the exhaust gases may be as high as about 45 %. Since the content in methane varies to a large degree, an integrated measurement really may depict to a considerable extent the variation in methane and, therefore, does not yield adequate information on true contamination. Therefore, the development and construction of combustion engines requires a more discriminating knowledge about the hydrocarbon content, and particularly it is necessary to learn more about the non-methane portion of the hydrocarbons.
The German Petty Patent No. 7403841 discloses a device for the methane-free measurement of hydrocarbon concentration in a gas by means of two FID's. They are constructed to receive two streams of sample gas whereby one of the gases contains all hydrocarbons, and the second stream contains only methane and a difference in measuring signals corresponding two of these hydrocarbon contents is formed in order to ascertain the non-methane protion in the hydrocarbon content. In this particular instance, the first FID has a flow delaying chamber disposed ahead of its gas inflow and a chamber containing a catalyst is disposed in the inflow path of the second FID. All higher hydrocarbons of the respective gas sample are combusted in that catalytic chamber, except the methane. The system uses as oxidizer the oxygen content in the respective sample gas. The catalyst is a copper oxide compound. It was found, however, that this particular device offers difficulties concerning the separation by the catalyst of the methane and the other hydrocarbons. Moreover, the catalyst becomes increasingly useless and the metal tube containing the catalyst must be exchanged accordingly. This amounts to an interruption in the measuring process.